1. Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly, to a display device having a pixel comprising red-color, green-color, blue-color, and white-color sub-pixels and a driving method thereof.
2. Discussion of the Related Art
Until recently, display devices generally employed cathode-ray tubes (CRTs) or television monitors. Presently, many efforts are being made to study and develop various types of flat panel displays, such as liquid crystal display devices (LCDs), plasma display panel (PDPs), field emission displays, and electro-luminescence displays (ELDs), as substitutions for CRTs because of their high resolution images, lightness, thin profile, compact size, and low voltage power supply requirements. In general, such a display device displays video information with a plurality of pixels arranged in a matrix type, and a pixel has red-color, green-color, and blue-color sub-pixels. In addition, in a display device, a pixel has red-color, green-color, blue-color and white-color sub-pixels.
FIGS. 1A and 1B are views of pixel arrangements according to the related art. In FIG. 1A, an RGB pixel arrangement includes red-color, green-color and blue-color sub-pixels, “R”, “G”, and “B”, arranged along a row to constitute a first pixel Pa. The first pixel Pa has a pixel area A. Thus, a size of each of the sub-pixels in the RGB arrangement is ⅓ A. In addition, the red-color, green-color and blue-color sub-pixels, “R”, “G”, and “B”, have a red-color filter, a green-color filter, and a blue-color filter formed therein, respectively. Further, the RGB arrangement emits white light by emitting red-color, green-color and blue-color light together. Thus, when light luminance is “Y” and transmittance of the color filters is ⅓, the luminance output of the pixel Pa is Y×⅓ for red-color, green-color, blue-color, and white-color light. Thus, assuming the luminance output of the RGB pixel arrangement 1, Y=3.
In FIG. 1B, an RGBW pixel arrangement includes red-color, green-color, blue-color, and white-color sub-pixels, “R”, “G”, “B”, and “W”, arranged along a row to constitute a second pixel Pb. The second pixel Pb also has the same pixel area A as the first pixel Pa. Thus, a size of each of the sub-pixels in the RGBW arrangement is ¼ A. That is, the sub-pixel size ratio between the RGBW arrangement and the RGB arrangement is 1:¾. As a result, the luminance of the red-color, green-color, and blue-color sub-pixels in the RGBW arrangement is ¾ of the luminance of the red-color, green-color, and blue-color sub-pixels in the RGB arrangement.
However, the white-color sub-pixel in the RGBW pixel arrangement does not have a color filter. Thus, light luminance is outputted through the white-color sub-pixel without reduction by a color filter. That is, the white luminance output in RGBW arrangement is {Y×⅓×0.75}(contribution of R, G, and B)+{Y×0.25}(contribution of W). Assuming the white luminance output of the RGB pixel arrangement 1 and Y=3, the white luminance output in the RGBW arrangement is (3×⅓×0.75+3×0.25)=1.5. As a result, the white luminance of the RGBW arrangement is 1.5 times brighter than the white luminance of the RGB arrangement.
FIGS. 2 and 3 are views of color space of the pixel arrangements in FIGS. 1A and 1B, respectively. In FIG. 2, light luminance of red-color, green-color and blue-color sub-pixels in the RGB pixel arrangement shown in FIG. 1A, “r′”, “g′”, and “b′”, have the same luminance value. Thus, the color space of the RGB pixel arrangement is a cubic region.
In FIG. 3, light luminance of red-color, green-color and blue-color sub-pixels in the RGBW pixel arrangement shown in FIG. 1B, “r”, “g”, and “b” also have the same luminance value. However, the color space of the RGBW pixel arrangement is a hexahedron region having a third quarter volume as many as the RGB color space along a line “0-w” from “w” to “2w,” the hexahedron region {(0, 0, 0), (r, 0, 0), (0, g, 0), (0, 0, b), (r, g, 0), (r, 0, b), (0, g, b), and (r, g, b)(or w)} in RGB coordinates because the RGBW color space has higher white luminance than red, green, and blue luminance.
FIG. 4 is a view of an RG-plane projection of color spaces in FIGS. 2 and 3. In FIG. 4, “e” corresponds to a line linking ((r, g, b)(or w)+(0, g, b)) and ((r, g, b)(or w)+(0, g, 0)) in FIG. 3. “f” corresponds to a line linking ((r, g, b)(or w)+(r, 0, b)) and ((r, g, b)(or w)+(r, 0, 0)) in FIG. 3.
In FIG. 4, “0-r′-w′-g′” region is a color space in RGB arrangement, “0-r-f-2w-e-g” region is a color space in RGBW arrangement. White luminance in RGBW arrangement is higher than in RGB arrangement, and red, green, and blue luminance in RGBW arrangement is lower than in RGB arrangement. White luminance is higher than red, green, and blue luminance in RGBW arrangement. Therefore, inequality of color luminance is generated.